This invention relates generally to emergency drench shower and eyewash stations of the type wherein cold and hot water supplies are thermostatically blended to provide a tempered discharge outflow at a selected temperature. More particularly, this invention relates to an improved tempered water mixing system having control means for assuring substantial water discharge, without risk of scalding the user, in the event of a main thermostatic mixing valve malfunction.
Tempered water mixing systems are used in a variety of commercial and/or industrial applications, e.g., in emergency drench shower stations and/or safety eyewash stations used to rinse hazardous chemicals from a person's skin and clothing or to extinguish burning clothing on a person. A typical system includes a thermostatic mixing valve adapted to thermostatically and automatically blend in-flowing hot and cold water streams to produce a mixed, tempered water output stream having a selected temperature, e.g., 80.degree. F.
A known problem with such tempered water mixing systems is that their thermostatic mixing valves may malfunction. As noted in U.S. Pat. No. 5,350,112, issued Sep. 27, 1994 to M. I. Stein, the malfunction can occur in any one of several modes. In one mode, the main thermostatic mixing valve is stuck or fails in a state or position that allows unregulated full flow of hot water, resulting in potentially dangerous scalding of a person using an emergency shower or eyewash station. In another mode, the mixing valve is stuck or fails in a state or position such that it allows unregulated full flow of cold water, whereby a person using an emergency shower or eyewash station may be subjected to undesirably cold water flow. This particular malfunction mode tends to result in a shortened flush or rinse time which is not desired since it can contribute to hypothermia in installations located in a cold weather climate. A third failure mode is one which results in insufficient flow of hot or cold water, whereby the rate of flow of the discharged water stream is inadequate for proper rinsing of contaminants from a person or extinguishing a person's burning clothing.
As noted in said U.S. Pat. No. 5,350,112, some tempered water mixing systems have been designed with back-up features intended to address the failure modes noted above. Those systems that use solenoid operated valves in combination with various temperature switches and/or flow rate switches for bypassing cold water flow past the main mixing valve when a malfunction occurs suffer from the limitation that they rely upon electrical power to achieve proper back-up operation. Hence such back-up devices tend to malfunction in the event of an electrical power failure. Further, electrically powered back-up devices may be unacceptable for use in proximity with volatile materials.
U.S. Pat. No. 5,350,112 discloses and claims an improved tempered water mixing system with fail-safe features, the claimed system being characterized by providing in the hot water supply line a temperature limit control valve that is coupled to and responds to a temperature sensor that is coupled to the system's mixed (tempered) water discharge conduit. Notwithstanding the system provided by U.S. Pat. No. 5,350,112, there still exists a need for further improvements in tempered water mixing systems for emergency drench shower and eyewash stations, particularly to satisfy the requirements of ANSI Standard 2358.1 which identifies the procedure for testing emergency shower and eye wash stations.